Packets produced on a packing machine are normally quality controlled to determine any defects, in particular, stains, scratches, or dents; and any faulty packets are subsequently rejected.
In U.S. Pat. No. 4,912,554, a packet is fed along a path through a quality control station where television cameras acquire an image of the packet; and the image is compared with a reference image to determine whether or not the packet is to be rejected.
Though efficient, the known quality control system described above has been found to fall short in some respects in terms of versatility and sensitivity. In particular, whenever changes are made to the graphics (artwork, brands, and/or colours) on the outside of the packets (e.g. so-called “brand changes”), changes must also be made to the reference image. Moreover, in areas of the packet bearing complex and/or highly coloured images, defects such as scratches or dents are especially difficult to detect. In other words, the artwork and colours on the packet act as noise during detection.
U.S. Pat. No. 5,877,506 discloses a device, which is designed to monitor blanks and comprises a source of infrared radiation. Such a device is designed to monitor only the contours of the blanks in order to verify the supply of the correct blanks, when there is a change in the type of packaging to be manufactured, and the correct positioning of the blanks. The device disclosed in U.S. Pat. No. 5,877,506 is not designed to control the quality of the blanks and is not designed to monitor surfaces of the blanks.